A Comparison of the Diets of Hatchery and Wild Coho Salmon (Oncorhynchus kisutch) in the Strait of Georgia from 1997-2007

摘要

Wild and hatchery-reared coho salmon (Oncorhynchus kisutch) have now co-existed in the Strait of Georgia for over 30 years, and have exhibited considerable variation in marine survival rates. This study is the first to compare diets of juvenile hatchery and wild coho salmon during the critical early marine period of this species. From 1997-2007, over 10,000 stomachs from juvenile coho salmon captured in the Strait of Georgia were examined. Diets in July were dominated by decapods (primarily crab megalops) and fish (primarily herring). In September, euphausiids and amphipods (primarily hyperiids) dominated. The variability between hatchery and wild coho salmon diet was larger in September than in July. Prey volume, stomach fullness and fork length were significantly correlated between hatchery and wild coho salmon in the July and September surveys. While coho salmon captured in September surveys had significantly higher percentages of empty stomachs than those from July, there were no significant differences in the percentage of empty stomachs between hatchery and wild coho salmon in either survey. Shifts in diet composition occurred both annually and seasonally, but the trends for both groups of coho salmon were the same. Thus, we conclude there were no significant differences observed between hatchery and wild coho salmon in either appetite (volume of prey in the stomach) or in diet (composition of stomach contents) in either July or September surveys from 1997-2007 in the Strait of Georgia, British Columbia, Canada.